The objective of this project is to study the interlocking and putative role of serine on the metabolism of homocysteine which has been identified as an indicator of arteriosclerosis. Specifically our investgations have addressed the questions: (1) what control is exerted over serine metabolism relative to the conversion of its beta-carbon atom to one-carbon units of metabolism, (2) what control is exerted over serine's role in the metabolism of sulfur containing amino acids. A second theme of our research involves studies on enzymatic reaction mechanisms on those enzymes requiring both pyridoxal-phosphate and folic acid for catalysis. We used our purified homogeneous enzymes to determine the kinetics, to investigate the stereochemistry, to isolate covalent intermediates, and finally to identify enzymatic groups involved in catalysis by site-specific reagents.